The government has written to health chiefs reminding them they have the power to order water companies to add fluoride to water supplies.

The move is being seen as a concerted effort to push for more fluoridation of drinking water.

Supporters, including the British Dental Association, say fluoridation help to cut tooth decay significantly.

But opponents claim fluoride can cause a range of problems, from tooth mottling to cancer.

MPs approved legislation to make it easier for fluoride to be added to drinking water in England and Wales in 2003.

Forcing people to ingest something against their will is a contravention of medical ethics

Carolyn Smith

Water companies have been allowed to add fluoride to supplies since 1985, but few have for fear of legal action.

The 2003 legislation gave health agencies the power to force firms to fluoride water after consulting local people, in order to tackle tooth decay.

In the latest move, the government's chief dental officer Professor Raman Bedi has written to health chiefs to tell them that adding fluoride to water supplies was a way to reduce health inequalities.

His letter explains the legal procedures that health authorities would need to follow to instruct water companies to fluoridate supplies.

Under the regulations, health authorities would have to test public opinion through a survey and focus groups before pushing ahead.

A Department of Health spokesperson said: "Water fluoridation is one of the more efficient and cost-effective of possible oral health promotion measures."

A spokesperson for the British Dental Association said: "It's tragic that, in the 21st century, there are still children as young as five having most or even all of their teeth removed under general anaesthetic as the result of tooth decay.

"Water fluoridation is a positive step in narrowing the health inequalities that currently exist."

"We are pleased that the guidelines for consultation have now been distributed to Strategic Health Authorities and look forward to open and honest debate as those consultations move forward."

Opponents concerned

However, Carolyn Smith, of the National Pure Water Association, said reading Professor Bedi's letter had "made her go cold".

She said fluoride had never been licensed as a medical treatment, and cited a US study which linked fluoridation to an increased risk of the childhood cancer osteosarcoma.

She told the BBC News website: "Forcing people to ingest something against their will is a contravention of medical ethics."

Fluoride is present naturally in most water supplies - but usually not at levels which are beneficial for dental health.

Currently, six million people in the UK - including the Midlands, Newcastle and the North East - receive fluoridated water supplies.